Exhaust and emissions
What is an oxygen sensor and when does it fail?
The oxygen sensor, also called a lambda sensor, sits in the exhaust and tells the control unit whether the air-fuel mixture is rich or lean so it can correct it instantly. The one before the catalytic converter controls the mixture and the one after it monitors the converter. When it fails, fuel consumption usually goes up and the check engine light comes on.
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How does it work?
It compares the oxygen in the exhaust with the outside air. Classic sensors give a voltage that switches between low (lean) and high (rich); wideband sensors measure the exact ratio and are increasingly common, diesels included.
They have to be very hot to work, so they carry an electric heater, which has its own codes.
What do bank and sensor mean in the codes?
Sensor 1 is upstream of the catalytic converter and sensor 2 downstream. Bank 1 is the side of the engine with cylinder 1; inline engines only have bank 1.
Why does it fail?
Age, contamination from burned oil or coolant, impacts, damaged wires or connectors and heater failures. An exhaust leak ahead of the sensor also skews its reading.
Many oxygen sensor codes are not about the sensor: a lean mixture from a vacuum leak makes the sensor tell the truth and the control unit store a code. That is why it is worth testing before replacing it.
What symptoms does it cause?
Higher fuel consumption, rough idle, a rotten egg smell from the exhaust, emissions over the limit at inspection and the check engine light on. Over time, a poorly controlled mixture can damage the catalytic converter.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
Related
Related trouble codes
- P0130O2 sensor (bank 1, sensor 1), circuit: malfunction
- P0133O2 sensor (bank 1, sensor 1), circuit: slow response
- P0135O2 sensor heater (bank 1, sensor 1), circuit: malfunction
- P0136O2 sensor (bank 1, sensor 2), circuit: malfunction
- P0141O2 sensor heater (bank 1, sensor 2), circuit: malfunction
- P0171Mixture too lean (bank 1)
Related symptoms
- Car uses more fuel than normal: causes and what to check
- Engine warning light on and steady: what it means and what to do
- Rotten egg smell from the car: what it means
Learn more
See what your car is saying
With the ECO-LITE, your workshop sees the oxygen sensor codes and, if the car publishes them, its voltage and the fuel trims live, remotely.
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Frequently asked questions
Can I drive with a faulty oxygen sensor?
Usually yes for a short time, but you will use more fuel and can damage the catalytic converter. Take it to a workshop soon.
How often should the oxygen sensor be replaced?
There is no universal interval: it depends on the engine and use. Replace it when it fails, after testing it.
Do diesels have an oxygen sensor?
Many modern diesels have a wideband sensor and, if they have SCR, NOx sensors.